Physics of coral as an indicator of reef health

Date:
December 14, 2021
Source:
Stanford University
Summary:
New research shows that physics measurements of just a small
portion of reef can be used to assess the health of an entire reef
system. The findings may help scientists grasp how these important
ecosystems will respond to a changing climate.



FULL STORY ==========================================================================
Vast amounts of energy flow around the ocean as waves, tides and currents, eventually impacting coasts, including coral reefs that provide food,
income and coastal protection to more than 500 million people. This
water movement is foundational to reef success, bringing nutrients and
food and removing waste, yet far less research has been focused on the
physics in comparison to the biology of these living communities.


========================================================================== Stanford scientists recently addressed this imbalance by demonstrating
that measuring the physics of just a small portion of reef with a
single instrument can reveal insights about the health of an entire
reef system. The findings point to low-cost methods for scaling up
monitoring efforts of these enigmatic living structures, which are at
risk of devastation in a changing climate. The results appeared in the
Journal of Geophysical Research: Oceans Dec. 14.

"This approach is like building a weather station for coral reefs,"
said lead study author Mathilde Lindhart, a PhD student in civil and environmental engineering. "If we have a couple of weather stations
around, we can then determine the weather everywhere on the reef."
Limited resources For decades, marine scientists have often relied
on a single instrument to calculate the flow around reefs because the measurements must be made with limited time and costly tools that can
only be anchored in certain locations.

As a result, they have had to assume that one measurement is
representative of flow over the entire reef. This new work confirms
that assumption is correct, bringing renewed credibility to previously collected data.

"Replication is the foundation of our ability to trust science," said
senior study author Rob Dunbar, a professor of Earth system science in Stanford's School of Earth, Energy & Environmental Sciences (Stanford
Earth). "Our results are building a solid foundation for other studies of
coral reef physics." The study authors tested a suite of current meters,
which send out sound waves that scatter off the currents and suspended particles, including sediment and plankton, then return with a shift in frequency that translates into flow velocities. They measured the fluid dynamics at different resolutions, with ranges from about 3 to 40 feet, depending on the instrument.



========================================================================== "Marine biologists that do research on specific fish or corals or other organisms need to measure the flow," said study co-author Alexy Khrizman,
a PhD student in Earth system science. "It's very important to know that
the choice of the instrument is not going to affect the research. It's
also important that we get the flow and turbulence work correct, otherwise
our calculations of production and calcification will not be correct." Serendipitous science The researchers conducted field work in different locations within the Salomon Atoll in the Chagos Archipelago in the
Indian Ocean, south of the Maldives.

They were collecting data about a reef off I^le Anglaise as part of a
larger initiative to study the British Indian Ocean Territory Marine
Protected Area when they realized they were prepared to test the
assumption that one instrument would provide enough information to
understand the flow of the entire reef.

"We were sort of testing our toolbox," Lindhart said. "We had all
these instruments in the water already and were actually looking for
something else - - it's rare that you have the opportunity to measure
the same thing, but in different ways." The researchers used the data
they collected to construct a three-dimensional model of the reef and
its flow, bringing new clarity to the life of these underwater cities.



========================================================================== "This is the first three-dimensional construct that tells us how the
roughness and its variability from place to place impacts water flow
over the reef," Dunbar said. "There's a direct correlation between
the roughness of the coral reef and the biodiversity of the reef."
Fundamental insights Through their research, the study authors aim
to answer foundational questions about how these incredibly complex
structures interact with incoming energy.

"There are so many ways to study reefs, what we sometimes call the
currency by which you're going to see what's going on. For most people,
it's fish or the corals themselves," Dunbar said. "What's really new is
that our currency is different -- this paper is about using the physics
of moving water as currency." They also hope the findings will be useful
to conservation managers. Coral reefs are like "super-efficient cement factories," according to Dunbar, producing architectures and buildings
that are self-healing. Although they comprise less than 1 percent of
the surface area of the ocean, reefs are home to about 25 percent of
all marine life.

"In order to make any kind of projection about climate change, we need to
know how they are working right now," Lindhart said. "The beautiful thing
about physics is that it's the same everywhere -- once we've established
some principles, you can take them and use them somewhere else."
Dunbar is the W.M. Keck Professor at Stanford Earth and a senior fellow
at the Stanford Woods Institute for the Environment. Study co-authors
include Stephen Monismith, the Obayashi Professor in the School of
Engineering, and David Mucciarone, lab manager in the Department of
Earth System Science.

This research was supported by the Bertarelli Program in Marine Science,
a Stanford Graduate Fellowship, the Gerald J. Lieberman Fellowship and
National Science Foundation grant OCE-1948189.

========================================================================== Story Source: Materials provided by Stanford_University. Original
written by Danielle Torrent Tucker. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. M. Lindhart, S. G. Monismith, A. Khrizman, D. Mucciarone,
R. Dunbar. How
Consistent Are Estimates of Roughness Parameters on a Rough
Coral Reef? Journal of Geophysical Research: Oceans, 2021; 126
(12) DOI: 10.1029/ 2021JC017825 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211214104245.htm

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